CARBON SOURCES 133 



this fungus to synthesize lactase, for this fungus makes good growth on 

 either glucose or galactose. The same argument applies to Blakeslea 

 trispora, Fusarium lycopersici, Rhizopus nigricans, and R. suinus. Non- 

 utilization of a complex carbohydrate is usually due to the lack of the 

 necessary hydrolytic enzymes. 



The hydrolysis of oligosaccharides by fungi is easily demonstrated. 

 Phycomyccs blakesleeanus utilizes sucrose while Mucor ramannianus does 

 not. If the mycelium of P. blakesleeanus is removed from a flask of 

 sucrose medium after several days' incubation and the flask reinoculated 

 with M. ramannianus, the latter fungus will grow. P. blakesleeanus 

 excretes sucrase, which catalyses the hydrolysis of sucrose to D-glucose 

 and D-fructose, both of which are utilized by M. ramannianus. 



A complex carbohydrate and its hydrolytic products are not necessarily 

 equivalent in all respects. Hawker (1947) reported that the amount of 

 mycelium produced by Melanospora destruens was different when this 

 fungus was grown on equivalent amounts of glucose, fructose, mixtures of 

 glucose and fructose, and sucrose. More mycelium was produced from 

 glucose than from an equivalent amount of sucrose, and this was true 

 whether the concentrations of these sugars were low or high. On the 

 other hand, perithecia were produced more abundantly on sucrose than 

 on glucose media. Indeed, hydrolysis of the same lot of sucrose to 

 glucose and fructose allowed the production of no more perithecia than 

 other samples of these sugars. The conclusion seems inescapable that 

 the particular structure of sucrose was in some way favorable for the pro- 

 duction of perithecia. While a fungus may utilize an oligosaccharide and 

 its hydrolytic products, it is not safe to assume that both are used with 

 the same efficiency for all purposes. 



POLYSACCHARIDES 



The chemistry of the polysaccharides resembles that of the oligosac- 

 charides except that the number of sugar residues is much larger. These 

 substances constitute the bulk of carbohydrate materials synthesized by 

 plants and animals. The most important polysaccharides are cellulose, 

 starch, and glycogen. On hydrolysis simple sugars are formed. The 

 molecular weights of polysaccharides may be very large; cellulose from 

 different sources may have a molecular weight ranging from 200,000 to 

 400,000. The molecular weights of many polysaccharides are much less 

 than that of cellulose. In general, polysaccharides are insoluble or only 

 colloidally soluble. The utilization of these substances by fungi is 

 dependent upon the excretion of the necessary hydrolytic enzymes. Pig- 

 man and Goepp (1948) classify polysaccharides on the basis of the 

 hydrolytic products as homopolysaccharides, which yield only one mono- 

 saccharide on hydrolysis, and heteropolysaccharides, which yield two or 



